This invention relates to an impact modifier for thermoplastic resins, a thermoplastic resin composition using the same, and an molded article obtained therefrom.
Heretofore, in order to improve impact resistance of thermoplastic resin compositions, there have been compounded conjugated diene rubber graft copolymers (e.g. MBS resin, ABS resin).
For example, vinyl chloride type resins are widely used for their advantages in flame retardancy, chemical resistance, etc. But the vinyl chloride type resins have a defect in that the resins by themselves are poor in impact resistance. Thus, the vinyl chloride type resins are compounded with impact modifiers. But even if a methyl methacrylate resin, MBS resin or ABS resin is simply mixed with a commercially available vinyl chloride type resin, the resulting molded article is not sufficient in impact resistance due to poor dispersibility of individual components.
In order to overcome this defect, it is proposed to use a graft copolymer of conjugated diene rubber with a methyl methacrylate copolymer obtained by suspension polymerization and having a suitable reduced viscosity (e.g. Japanese Patent Unexamined Publication Nos. 60-161450 and 61-14246). But since such a conjugated diene rubber component has many double bonds which are chemically unstable in the main chain, the graft copolymer is readily deteriorated by ultraviolet rays, which results in making the outdoor practical use impossible due to poor weathering resistance such as lowering in strength, causing discoloration, and the like.
In order to improve the weathering resistance, it is proposed to use a methyl methacrylate series polymer and a graft copolymer obtained by grafting an acrylic acid alkyl ester, a methacrylic acid alkyl ester, an aromatic vinyl compound, a vinyl cyanide compound, and the like in the presence of an acrylic rubber containing almost no double bonds in the main chain (Japanese Patent Unexamined Publication No. 59-98153). But according to this proposal, the weathering resistance can be improved to some extent, but there arises a problem of lowering impact resistance.
The methyl methacrylate series polymer used in the above proposal is excellent in weathering resistance but is poor in flame retardancy, impact resistance, chemical resistance and solvent resistance. Thus, when the methyl methacrylate series polymer is mixed with a vinyl chloride series resin, inherent properties of the vinyl chloride series resin are damaged.
As mentioned above, it was impossible to provide thermoplastic resin compositions well balanced in properties such as impact resistance, weathering resistance, etc.